Abstract
Bloodstream infections (BSIs) are a major cause of morbidity and mortality among burn patients. The microbiological spectrum and resistance patterns of burn-related BSIs are strongly influenced by local antibiotic usage and infection control practices, underlining the need for institution-specific data. This descriptive cross-sectional study was conducted in a tertiary care hospital in India to characterise the microbiological profile and antimicrobial resistance patterns of BSIs in burn patients. Blood cultures from 66 hospitalised burn patients were processed using standard microbiological methods, of which 25 yielded significant growth. Acinetobacter baumannii was the most frequently isolated pathogen, followed by Pseudomonas aeruginosa and Staphylococcus aureus. BSIs were significantly associated with flame burns, deep burns, diabetes mellitus, prolonged hospitalisation, and high levels of antimicrobial resistance, particularly among Gram-negative organisms. These findings emphasise the importance of locally generated antibiograms and targeted antimicrobial stewardship to guide empirical therapy and improve outcomes in burn patients.
Introduction
Burn injuries remain a major global public health concern.1,2 These injuries compromise the ability of skin to function as body's primary barrier against microbial invasion, and wound colonisation by microorganisms begins within hours of injury. If not treated readily and effectively, this colonisation can progress to local infection and further leads to systemic involvement, including bloodstream infection (BSI) and sepsis.3,4 This results in increased morbidity, prolonged hospitalisation, higher healthcare expenses, and mortality.3,5 BSIs may further be promoted by, invasive procedures such as central venous catheterisation, 6 among other factors.
Infection with multidrug-resistant bacteria is common and the administration of broad-spectrum antibiotics creates a selective antibiotic pressure. 7 The microbiological landscape of BSIs in burn patients is dynamic and region-specific, often influenced by local antibiotic usage patterns, infection control practices, and environmental microbial flora. 8 Common causative organisms include Gram-negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii, as well as Gram-positive organisms such as Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) strains9,10 and often exhibit high levels of antimicrobial resistance, highlighting the need for robust local microbiological surveillance.7,11,12 Therefore, the present study was undertaken to determine the prevalence of BSIs in burn patients and to characterise the causative pathogens, their antimicrobial susceptibility patterns, and associated risk factors and outcomes.
Materials and methods
Our descriptive cross-sectional study was conducted from January to December 2024 in the Department of Microbiology and Burns & Plastic Surgery Department, University College of Medical Sciences and Guru Teg Bahadur, Hospital, Delhi. Considering the microbiological BSI rates as 22% (an average from two previous studies7,13), blood cultures were collected from 66 subjects as an adequate sample size.
We included patients aged above 12 years admitted with a total burn surface area of >20%, and excluded any patients treated as out-patients.
Blood cultures were obtained using standard aseptic technique. In total, 70% alcohol was used to disinfect the area of venepuncture and allowed to dry for 30 s. Chlorhexidine/povidone iodine was used to disinfect the site concentrically, inside out, and was allowed to dry for 10 min. After drying the cap of the bottle with an alcohol wipe, blood collected aseptically was injected into the bottle without changing the needle. A total of 10 ml of blood per adult bottle (BacT/Alert FA plus bottle) was collected and sent immediately to the microbiology laboratory. If there was an unavoidable delay, inoculated bottles were kept at room temperature up to 24 h before loading into the instrument. True BSI was identified using a combination of clinical criteria and microbiological parameters, including results from paired blood culture samples and time to positivity, with early and concordant culture positivity supporting true infection, while isolates with delayed or discordant positivity were classified as probable contaminants to avoid overestimation of BSI burden.
A detailed history including age, days of hospitalisation, percentage of total body surface area (TBSA), depth of burns, diabetes, and hypertension, was taken. Burns were classified into superficial (involving only the epidermal layer of skin), partial thickness (involving the epidermis and portions of the dermis), and full-thickness (extending through and destroying all layers of the dermis and often injuring the underlying subcutaneous tissue). 14 For estimating the percentage of TBSA burned for risk factor analysis, the ‘Lund–Browder chart’ was followed. 15
Blood culture bottles were analysed by the BacT/Alert Microbial Detection System. Direct Gram stain from the positively flagged bottle was done and subsequent subculture was done on blood agar and MacConkey agar and incubated overnight at 37 °C. Growth on the media was identified by colony characteristics, Gram stain, motility, and conventional biochemical tests. Antimicrobial susceptibility of the isolates was evaluated by Kirby–Bauer disc diffusion method and zone size was interpreted according to the latest Clinical Laboratory Standard Institute (CLSI) standard guidelines. 16 Not all antibiotics were tested for every microorganism, and as part of the quality control process, Escherichia coli (ATCC 25922), S. aureus (ATCC 25923), and P. aeruginosa (ATCC 27853) control strains were used in the Kirby–Bauer disc diffusion method. Each antibiotic was tested with the control strain. Growth of three or more colony morphologies with no polymorphonuclear cells on Gram stain was excluded.
Data collected were recorded on a Microsoft Excel sheet. The prevalence of BSIs in burn patients was reported as percentage along with the proportion and distribution of the organisms. To study the risk factor, univariate analysis was done using t-test or unpaired t-test for qualitative/quantitative data, respectively. Odds ratio (OR) was calculated to assess the risk factor. Significance was defined as a p-value <0.05. Statistical analysis was performed using SPSS (version 20.0, IBM).
Ethical approval for this study was granted by the Institutional Ethics Committee for Human Research (IEC-HR) of the Guru Teg Bahadur Hospital Ethics Committee (Approval No. GTBHEC 2024/P-203, dated 26-04-2024).
Results
Of the 66 samples analysed, 34 (51%) showed no evidence of BSI, 25 (38%) were classified as true BSIs, and 7 (11%) were considered contaminants. Of the 25 BSI cases, 22 (88%) were monomicrobial and 3 (12%) were polymicrobial. Among the three polymicrobial blood culture reports, two revealed the presence of S. aureus in combination with A. baumannii, while the third showed S. aureus with P. aeruginosa.
A total of 66 blood culture specimens were collected from patients suspected of having invasive infection. Of these, 25 were culture positive, yielding 28 isolates (three polymicrobial infections). The most common isolate was A. baumannii (9, 32.1%), followed by P. aeruginosa (6, 21.4%) and MRSA (4, 14.3%). Other bacteria isolated included E. coli, Enterobacter species, K. pneumoniae, methicillin-sensitive S. aureus, and Candida species (Candida glabrata and Candida parapsilosis) (Fig. 1). Antibiotic susceptibility testing was performed for routinely used antibiotics according to the CLSI standards. Acinetobacter species exhibited greater resistance to all the tested antibiotics compared to Gram-negative isolates. P. aeruginosa exhibited the least resistance to imipenem and ceftazidime. Both K. pneumoniae isolates (2/2) were resistant to piperacillin–tazobactam and ceftriaxone. All E. coli and Enterobacter isolates showed resistance to ciprofloxacin, with the Enterobacter isolates additionally resistant to imipenem and piperacillin–tazobactam (Table 1).
Microbiological profile of blood culture samples in burn patients (n = 28).
Microorganisms-wise resistance pattern of Gram-negative bacteria to various antibiotics in the study group (n = 21).
NT: not tested.
All S. aureus isolates, including both MRSA (four isolates) and Methicillin-sensitive S. aureus (one isolate), demonstrated resistance to erythromycin, gentamicin, and ciprofloxacin (Table 2). Patients with invasive infections, blast injuries, flame burns, and self-inflicted burn injuries had significantly increased risk of invasive infection (OR = 6.65, p = 0.0019). A prolonged hospital stay of more than two weeks was also significantly associated with a higher likelihood of developing invasive infections (OR = 4.13, p = 0.0136). Burns involving >40% of TBSA had a higher OR, though this was not statistically significant. In contrast, deep burns showed a significant association with invasive infections (OR = 4.65, p = 0.0176) (Table 3).
Microorganisms-wise resistance pattern of Gram-positive bacteria to various antibiotics (n = 5).
MRSA: methicillin-resistant S. aureus.
Stratification of risk factors among burn patients with and without BSI (n = 59).
BSI: bloodstream infection; CI: confidence interval.
Mortality was significantly higher among patients with invasive infections (22/25; 88%) compared to those without BSIs (2/34; 5.88%), with an OR of 117.33 (p < 0.00001). The relationship between invasive BSIs and patient outcomes, including mortality, is detailed in Table 4.
Outcome of patients with and without BSI in the study group (n = 59).
BSI: bloodstream infection; CI: confidence interval.
Discussion
The mortality rate among burn patients with BSIs (88%) in our study was notably high and reflects the overall severity of illness rather than BSI alone. Patients who developed BSIs constituted a critically ill subgroup, characterised by deep or full-thickness burns, larger TBSA involvement, prolonged hospitalisation, flame or blast injuries, and a higher prevalence of diabetes mellitus – factors independently associated with poor outcomes in burn patients. In addition, BSIs were predominantly caused by multidrug-resistant Gram-negative pathogens, particularly A. baumannii and P. aeruginosa, which are linked to limited therapeutic options and adverse outcomes in burn units. The convergence of severe burn injury, invasive infection, and antimicrobial resistance likely acted synergistically to drive the high mortality observed.
It has been observed that >25% burn patients in Indian tertiary settings suffer BSIs, and many succumb early during intensive care unit stays. 17 These were more common with the size of burn and in diabetics, a trend previously well noted.7,18,19 Aggressive wound care, vigilant glucose management, and early infection surveillance are thus crucial for diabetic burn patients.
Bloodstream isolates demonstrated a markedly resistant antimicrobial susceptibility pattern, particularly with Acinetobacter spp. showing >90% resistance to all tested antibiotics, underscoring its dominance as a multidrug-resistant pathogen in burn units. The isolation of non-albicans Candida species (C. glabrata and C. parapsilosis) further highlights the shifting epidemiology towards fungal BSIs in critically ill burn patients. 16 Collectively, susceptibility patterns underline the critical importance of local antibiograms in guiding early, targeted therapy for BSIs and improving outcomes in high-risk burn patients.
Local antibiotic usage and infection control practices influence the microbiological profile and resistance patterns observed in our study. Prevention of infection with multidrug-resistant organisms is almost impossible for the more serious burn injuries and emphasises the need for continuous local surveillance, judicious antibiotic use, and reinforcement of infection control practices to control multidrug-resistant infections in burn patients. Although, the need and results of early debridement and skin grafting have not been taken into consideration, our observation of a predominance of multidrug-resistant pathogens reinforces that effective infection control in burns depends primarily on timely surgical source control through adequate debridement and early excision, rather than on the indiscriminate use of antibiotics.
Multiple studies have conclusively shown that early excision of devitalised tissue with prompt wound closure reduces microbial burden, limits progression from colonisation to invasive infection, decreases sepsis rates, and improves survival.20,21 This issue is particularly critical for low- and middle-income countries, including India, where early excision and grafting are not routinely practiced, and delays in wound closure continue to contribute substantially to infection-related morbidity and mortality.
21
Being a single-centre study, our results may not reflect the microbiological profile or resistance patterns in other hospitals or regions. The cross-sectional design captures data at a single point in time, preventing analysis of causal relationships or infection progression. Multivariable analysis was not performed due to limited sample size and outcome events, to avoid model overfitting. Potential biases may exist due to selective blood culture sampling or prior antibiotic exposure, which could influence culture positivity. Lastly, the absence of molecular testing for resistance genes may have underestimated the prevalence of certain resistance mechanisms. However, the broad conclusions of our report are inescapable.
Footnotes
Ethical considerations
Ethical approval for this study was granted by the Institutional Ethics Committee for Human Research (IEC-HR) of the Guru Teg Bahadur Hospital Ethics Committee (Approval No. GTBHEC 2024/P-203, dated 26-04-2024). The procedures followed the guidelines laid down in the Declaration of Helsinki, 1964, and as revised later.
Author contributions
Kirti Nirmal contributed to the conceptualisation and design of the study. Debamita Banik, Senjam Krishna Singha, and Hage Yaja were involved in data collection and laboratory work. Dhananjay Kumar contributed to clinical evaluation and patient management. Shukla Das provided overall supervision, critical review, and guidance throughout the study. All authors contributed to manuscript revision, read, and approved the final version of the manuscript.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data availability statement
The datasets generated or analysed during the study are not publicly available due to concerns regarding participant confidentiality and institutional data-sharing policies, but are available from the corresponding author upon reasonable request.
Statement on approval from all contributors
The manuscript has been read and approved by all the authors, that the requirements for authorship as stated earlier in this document have been met, and that each author believes that the manuscript represents honest work.